This is an issue we have seen a couple of times over the past few months. In most cases we have been able to edit the saved URL for your account(s) in Banktivity to the most recent URL for your banks website to resolve this issue.
To edit the URL for your account(s) you need to Double-Click on the Account name for the account itself from under “Accounts” (not under “Websites”). This will open a popup Account Inspector window. Inside the Account Inspector delete the existing URL entered beside “Website”. Next, go to your banks website using an external web browser application, like Safari or Firefox. Specifically go to the login page, if the login is separate from the main homepage. Then copy & paste the URL for your banks website from your web browser into the “Website” field in the Account Inspector for your account in Banktivity.
Please repeat this process with all accounts so all accounts have the latest URL. This should help to resolve any issues related to Flash Player when using the built in browser in Banktivity.
Alternatively, you could also try to uninstall Flash Player from your Mac. Here is a link to a page on how to uninstall Flash Player from the Adobe website: